FIG. 4 is a sectional view showing a conventional sealing structure for cross shaft (spider). The figure shows only a quarter (a second quadrant) of a cross shaft 1. The shaft 1 is employed by, for example, an automotive steering shaft and used under an environment exposed to water and mud spattered from a road surface. Referring to the figure, a vertical shaft 1v and a horizontal shaft 1h constituting the cross shaft 1 are each assembled with a cup-shaped outer ring 3 allowed to rotate by needle-like rollers 2. A ring-like seal 4 having a core bar 4a is fitted on a respective root portion of the vertical shaft 1v and the horizontal shaft 1h. The reason for using the seal 4 with the core bar is to establish a tight fit relation with the cross shaft 1 in order to ensure mud/water tightness of the seal. The adjoining core bars 4a are so arranged as to define a gap even between their portions in closest proximity to each other.
Because of the inclusion of the core bar, the seal 4 employed by the conventional sealing structure for cross shaft as described above is more expensive than a seal free from a core bar. However, the seal obviating the core bar for cost down is decreased in fastness to the cross shaft 1, so that the seal is liable to rotate in conjunction with the rotation of the outer ring 3. In this occasion, the seal suffers heavy wear at its base (a portion in contact with the cross shaft 1). As a result, the muddy water detrimentally enters through clearance between the base of the seal and the cross shaft 1.
In view of the foregoing problem encountered by the conventional art, it is an object of the present invention to provide a sealing structure for cross shaft which is not decreased in the mud/water tightness despite the omission of the core bar.